By doing a plasma treatment in which a material is made into plasma and then deposited on an object to be treated, a strong film can be formed on said object to be treated. In particular, when carbon is used as said material, a diamond-like carbon (DLC) film comprising an amorphous conglomerate of the diamond structure and the graphite structure can be obtained on the object to be treated. This DLC film has good mechanical, chemical, and optical properties.
As a method to make said material into plasma, there is a method in which said material is made into a cathode, and plasma is formed from said cathode by generating an arc discharge under vacuum between it and the trigger electrode that is an anode. The plasma formed this way is led from the plasma generating portion to a plasma advancing tube as a plasma stream in the plasma processing apparatus, introduced into the plasma processing portion, and used for the film treatment of the object to be treated.
In this arc discharge, at the same time as the plasma generation, cathode material particles called droplets, ranging in size from less than submicron up to several hundred microns, are also produced as a byproduct. When these droplets arrive at said plasma processing portion and adhere to the object to be treated, defects occur on the film of said object to be treated. Therefore, a means for removing these droplets is necessary to maintain the quality of said film.
As a droplets capture means, an annular rib placed in a plasma advancing tube is disclosed in the Japanese Patent Laid-Open No. 2008-91184 bulletin (Patent Document 1) and the Japanese Patent Laid-Open No. 2008-248347 bulletin (Patent Document 2).
FIG. 19 is a perspective diagram of this annular rib 140. Annular rib 140 has plasma advancing tube joining portion 141 and rib portion 142, and annular rib 140 is positioned by joining plasma advancing tube joining portion 141 with plasma advancing tube. The droplets generated in the plasma generating portion collide with rib 142, and are captured. On the other hand, the plasma stream passes through the open portion in the center of annular rib 140, and advances to the plasma processing portion.
Usually, rib 142 is inclined toward the upstream direction of said plasma stream in comparison to the central axis of said plasma advancing tube, and the efficiency of the capture of said droplets is improved by this inclination.
Said droplets are deposited on said annular rib. This deposited matter is extremely fragile, because the binding power between the constituent droplets is weak. Therefore, even if it falls from said annular rib, because it is crushed by the shock at the time of the fall, it does not remain in the plasma generating portion as a large-sized fragment.
It has been confirmed that this annular rib 140 contributes highly to the removal of droplets, and the plasma processing apparatus equipped with annular rib 140 has gained an industrial success.
[Patent Document 1] Japanese Patent Laid-Open No. 2008-91184 bulletin
[Patent Document 2] Japanese Patent Laid-Open No. 2008-248347 bulletin